Optical Element Stack Assemblies

ABSTRACT

The present disclosure describes optical element stack assemblies that include multiple substrates stacked one over another. At least one of the substrates includes an optical element, such as a DOE, on its surface. The stack assemblies can be fabricated, for example, in wafer-level processes.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of priority of U.S.Provisional Patent Application No. 62/063,532, filed on Oct. 14, 2014.The disclosure of the earlier application is incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to optical element stack assemblies.

BACKGROUND

Various optoelectronics modules are used, for example, for imagingapplications, such as three-dimensional (3D) imaging, or distancemeasurement applications, such as proximity sensing. In someapplications, an optical emitter assembly is operable to emit astructured optical pattern, which can be useful for imaging as well asdistance sensing applications. The structured light can result in apattern of discrete features (i.e., texture) being projected onto anobject. Light reflected by the object can be directed back toward animage sensor, where it is sensed. The sensed signals can be used fordistance calculations. In some cases, structured light providesadditional texture for matching pixels in stereo imaging applications.

In some modules, an optical element, such as a diffractive opticalelement (DOE), is introduced into the path of light emitted by a lightsource such as a vertical cavity semiconductor emitting laser (VCSEL) orVCSEL array. The DOE can be useful in creating the structured lightpattern. It also can facilitate multiplying a structured light patterngenerated by the VCSEL or other light source.

SUMMARY

The present disclosure describes optical element stack assemblies thatcan be fabricated, for example, by wafer-level methods.

For example, in one aspect, a wafer-level method of fabricating stackassemblies includes attaching a first wafer to a second wafer to form awafer sub-stack. At least one of the first wafer or the second wafer hasoptical elements on its surface. The first and second wafers areattached such that each optical element is disposed between the firstand second wafers. The method further includes attaching a spacer waferto the wafer sub-stack to form a wafer stack, and separating the waferstack into stack assemblies, each of which includes at least one of theoptical elements.

In another aspect, a wafer-level method of fabricating stack assembliesincludes providing first and second wafers, wherein at least one of thefirst wafer or the second wafer has optical elements on its surface. Themethod includes using a single vacuum injection technique to form upperand lower spacers on opposite surfaces of the second wafer. The methodfurther includes attaching the first wafer to the second wafer to form awafer stack. The first and second wafers can be attached such that eachoptical element is disposed between the first and second wafers. Thewafer stack then can be separated onto stack assemblies, each of whichincludes at least one of the optical elements.

In yet another aspect, a wafer-level method of fabricating stackassemblies includes providing first and second wafers, wherein at leastone of the first wafer or the second wafer has optical elements on itssurface. The method includes attaching the second wafer to a tape andseparating the second wafer into singulated substrates. The singulatedsubstrates are placed into a vacuum injection tool to form upper andlower spacers on opposite surfaces of the singulated substrates. Thefirst wafer is attached to the singulated substrates to form a stacksuch that each optical element is disposed between the first wafer andone of the singulated substrates. The stack then is separated into stackassemblies, each of which includes at least one of the optical elements.

The disclosure also describes a stack assembly including a firstsubstrate, a second substrate attached to the first substrate, and anoptical element on at least the first substrate or the second substrate,wherein the at least one optical element is disposed between the firstand second substrates. The stack assembly includes a first spacerattached to an outer side of the first or second substrate. In someimplementations, the stack assembly further includes a second spacerbetween the first and second substrates, wherein the first and secondspacers are part of the same vacuum injection molded piece. Also, insome cases, the vacuum injection molded piece laterally surrounds sideedges of the second substrate. Further, the first and second substratescan be attached to one another by adhesive on a lateral side portion ofone or more of the optical elements.

Various implementations include one or more of the following features.For example, each of the first and second wafers can have a respectiveoptical element on its surface, the optical elements facing one another.In some instances, the optical elements are diffractive opticalelements. In some implementations, the optical elements are replicatedoptical elements.

The wafer-level methods allow multiple assemblies to be fabricated inparallel at the same time. Further, the techniques can be usedadvantageously to provide for smaller or larger distances between thefirst and second wafers, depending on the application. Various examplesare described in greater detail below. Other aspects, features andadvantages will be readily apparent from the following detaileddescription, the accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first example of an optical element stack assembly.

FIGS. 2A-2F illustrate examples of steps in the fabrication of theoptical element stack assembly of FIG. 1.

FIG. 3 illustrates a second example of an optical element stackassembly.

FIGS. 4A-4F illustrate examples of steps in the fabrication of theoptical element stack assembly of FIG. 3.

DETAILED DESCRIPTION

The present disclosure describes optical element stack assemblies thatinclude multiple substrates stacked one over another. At least one ofthe substrates includes an optical element, such as a DOE, on itssurface. In some cases, both substrates have an optical element on theirrespective surfaces. The substrates, and optical elements, are alignedsuch that an optical signal passing through the stack passes through thesubstrates and the optical element(s).

As shown in FIG. 1, a stack assembly 10 includes first and secondsubstrates 12, 14 stacked one over the other. Each substrate 12, 14 canbe composed, for example of a glass, polymer or other material that istransparent to a specified wavelength or range of wavelengths (e.g., inthe visible, infra-red (IR) and/or near-IR parts of the spectrum). Inthe example of FIG. 1, the substrates 12, 14 have passive opticalelements 16, 18 formed on their opposing surfaces. In the illustratedexample, the optical elements 16, 18 are DOEs. Other types of passiveoptical elements (e.g., refractive or diffractive lenses, or arrays ofoptical elements, such as micro-lens arrays) can be provided in someimplementations. Further, in some cases, one substrate 12 may have atype of optical element that differs from the type of optical element onthe other substrate 14. In some instances, only one of the substrates12, 14 may have an optical element on its surface.

The lateral side portions 20 of the material forming the opticalelements 16, 18 can serve as spacers to provide a well-definedseparation ‘d’ between the opposing optical elements 16, 18. A typicalthickness ‘t’ of the lateral side portions 20 is 50 μm or less (e.g.,25-50 μm). In the illustrated example, the optical elements 16, 18 arecomposed of an epoxy material that is transparent to the specifiedwavelength or range of wavelengths. The substrates 12, 14 are connectedtogether by a thin layer of glue or other adhesive 22 disposed on thelater side portions 20. A typical thickness of the adhesive 22 is lessthan 10 μm (e.g., 7 μm). The dimensions mentioned above may differ insome implementations.

A thin non-transparent coating 24 on the optical-element side of the topsubstrate 14 defines an optical stop 26, which serves to define atransparent window through which light of the specified wavelength or inthe specified range of wavelengths can pass. An outer surface of eachsubstrate 12, 14 can be coated with a thin anti-reflective coating (ARC)28. The ARC-side of the bottom substrate 12 includes a spacer 30 toprovide a well-defined distance between the optical elements 16, 18 anda surface on which the assembly 10 is mounted. The spacer 30, which canbe fixed to the ARC-side of the bottom substrate 12 by adhesive, has anopening 32 below the stop 26.

FIGS. 2A-2F illustrate steps of a wafer-level method for manufacturingoptical element stack assemblies such as the assembly 10 of FIG. 1.Wafer-level processes allow multiple assemblies 10 to be fabricated atthe same time. Generally, a wafer refers to a substantially disk- orplate-like shaped item, its extension in one direction (z-direction orvertical direction) is small with respect to its extension in the othertwo directions (x- and y- or lateral directions). In someimplementations, the diameter of the wafer is between 5 cm and 40 cm,and can be, for example, between 10 cm and 31 cm. The wafer may becylindrical with a diameter, for example, of 2, 4, 6, 8, or 12 inches,one inch being about 2.54 cm. In some implementations of a wafer-levelprocess, there can be provisions for at least ten modules in eachlateral direction, and in some cases at least thirty or even fifty ormore modules in each lateral direction. To facilitate understanding, inFIGS. 2A-2F only a portion of each wafer corresponding to a singleassembly 10 is illustrated.

As shown in FIG. 2A, a first transparent wafer 114 is provided and hasan ARC 128 on a first surface and a non-transparent layer (e.g.,photoresist) 123 on its opposite second surface. The wafer 114 can becomposed, for example of a glass, polymer or other material that istransparent to the specified wavelength or range of wavelengths. Asshown in FIG. 2B, the layer 123 is patterned (e.g., using standardphotolithography techniques) to form regions 124 of non-transparentmaterial that define the non-transparent coating 24 for each assembly10.

Next, as shown in FIG. 2C, optical elements 118 (e.g., DOEs) are formedon the second surface of the substrate 114. The optical elements 118,one of which is shown in FIG. 1C, can be formed, for example, bywafer-level replication. In general, replication refers to a techniqueby means of which a given tool (the tool including e.g., a negative ofthe optical elements) structure or a negative positive thereof is usedto reproduced via, e.g., etching, embossing or molding a structuredsurface (e.g., a positive of the optical elements). In a particularexample of a replication process, a structured surface (e.g., definingan optical element or a plurality of optical elements) is pressed into aliquid, viscous or plastically deformable material by using a tool, thenthe material is hardened, e.g., by curing using ultraviolet radiationand/or heating, and then the structured surface tool is removed. Thus, areplica of the structured surface is obtained. Suitable materials forreplication are, for example, hardenable (e.g., curable) polymermaterials or other replication materials, i.e. materials which aretransformable in a hardening or solidification step (e.g., a curingstep) from a liquid, viscous or plastically deformable state into asolid state. The thickness of the yard portions 120 of the replicatedmaterial typically is 50 μm or less (e.g., 25-50 μm). The processing inFIGS. 2A-2C results in a first wafer subassembly 140 that provides thetop substrate 14 for each assembly 10.

As part of the fabrication process, a second transparent wafer 112 isprovided and has an ARC 128 on its first surface. Optical elements 116(e.g., DOEs), one of which is shown in FIG. 2D, are formed on the secondsurface of the wafer 112. The optical elements 116 also can be formed,for example, by wafer-level replication as described above. Theprocessing in FIG. 2D results in a second wafer subassembly 150 thatprovides the bottom substrate 12 for each assembly 10.

Next, as shown in FIG. 2E, the first and second wafer subassemblies 140,150 are attached to one another to form a wafer sub-stack 160. Thesubassemblies 140, 150 can be attached to one another, for example, byglue or other adhesive (e.g., by glue setting or screen printing). Thesubassemblies 140, 150 can be attached to one another such that theoptical elements 116, 118 face one another. Further, as shown in FIG.2F, a spacer wafer 130 is attached to the ARC-side of the second waferassembly 140 to complete the wafer stack 170. The spacer wafer 130 canbe attached, for example, by glue or other adhesive. Once thewafer-level stack 170 is completed, it can be separated (e.g., bydicing) to form multiple individual assemblies 10.

In the example process of FIGS. 2A-2F, both wafers 112, 114 have opticalelements 116, 118 replicated on their respective surfaces. In someimplementations, however, only one of the wafers (either the first wafer114 or the second wafer 112) has optical elements on its surface.Further, although the optical elements 116, 118 are shown as DOEs, othertypes of optical elements can be used in some instances.

FIG. 3 illustrates a second example of an optical element stack assembly300. The stack assembly 300 includes first and second substrates 312,314 stacked one over the other. Each substrate 312, 314 can be composed,for example of a glass, polymer or other material that is transparent toa specified wavelength or range of wavelengths (e.g., in the visible,infra-red (IR) and/or near-IR parts of the spectrum).

In the example of FIG. 3, the substrates 312, 314 have passive opticalelements 316, 318 formed on their opposing surfaces. In the illustratedexample, the optical elements 316, 318 are DOEs. Other types of passiveoptical elements (e.g., refractive or diffractive lenses) can beprovided in some implementations. Further, in some cases, one substrate312 may have a type of optical element that differs from the type ofoptical element on the other substrate 314. In some instances, only oneof the substrates 312, 314 may have an optical element on its surface.

A thin non-transparent coating 324 on the optical-element side of thetop substrate 314 defines an optical stop 326, which serves as atransparent window through which light of the specified wavelength or inthe specified range of wavelengths can pass. An outer surface of eachsubstrate 312, 314 can be coated with a thin anti-reflective coating(ARC) 328.

To increase the separation ‘d’ between the opposing optical elements 16,18, a vacuum injection molded spacer 380 separates the lateral sideportions 320 of the material forming the optical elements 316, 318. Thespacer 380 can be fixed directly (without adhesive) to the lateral sideportion 320 of the optical element 316 on the bottom substrate 312. Thespacer 380 can be attached to the lateral side portion 320 of theoptical element 318 on the top substrate 314 by glue or other adhesive322. The ARC-side of the bottom substrate 312 includes a spacer 390 toprovide a well-defined distance between the optical elements 316, 318and a surface on which the assembly 300 is mounted. The spacer 390 canbe a vacuum injection molded spacer, which can be fixed directly to theARC-side of the bottom substrate 312 (i.e., without adhesive). Thespacer 390 has an opening 332 below the stop 326.

As illustrated in FIG. 3, the spacers 380 and 390 can be formed as asingle vacuum injection molded piece, part 392 of which surrounds thelateral side edges 394 of the bottom substrate 312.

FIGS. 4A-4F illustrate steps of a wafer-level method for manufacturingoptical element stack assemblies such as the assembly 300 of FIG. 3.FIGS. 4A-4C show a process for forming a first wafer subassembly 440that provides the top substrate 314 for each assembly 300. This part ofthe process can be substantially the same as the corresponding steps inFIGS. 2A-2C. Thus, as shown in FIG. 4A, a first transparent wafer 414 isprovided and has an ARC 428 on a first surface and a non-transparentlayer (e.g., photoresist) 423 on its opposite second surface. The wafer414 can be composed, for example of a glass, polymer or other materialthat is transparent to the specified wavelength or range of wavelengths.As shown in FIG. 4B, the layer 423 is patterned (e.g., using standardphotolithography techniques) to form regions 424 of non-transparentmaterial that define the non-transparent coating 324 for each assembly300.

Next, as shown in FIG. 4C, optical elements 418 (e.g., DOEs) are formedon the second surface of the substrate 414. The optical elements 418,one of which is shown in FIG. 4C, can be formed, for example, bywafer-level replication, as discussed above. The processing in FIGS.4A-4C results in a first wafer subassembly 440 that provides the topsubstrate 314 for each assembly 300.

As part of the fabrication process, a second transparent wafer 412 alsois provided and has an ARC 428 on its first surface (FIG. 4D). Initialpreparation and processing of the second wafer 412 can be similar tothat of wafer 112 in FIG. 2D. Thus, optical elements 416 (e.g., DOEs),one of which is shown in FIG. 4D, are formed on the second surface ofthe wafer 412. The optical elements 416 also can be formed, for example,by wafer-level replication as described above.

Next, as illustrated in FIG. 4E, second wafer subassembly 450 is subjectto formation of through-holes and a vacuum injection molding processthat fills the through-holes and forms the top and bottom spacers 380,390. Thus, the spacers 380, 390 can be formed as a single vacuuminjection molded piece, part 392 of which fills though-holes in thesecond wafer 412. Suitable techniques are described in U.S. Pat. No.9,094,593 and in U.S. Published Patent Application No. 2015-0034975. Thetechniques include forming through-holes through a wafer, for example,by dicing, micromachining or laser cutting. Vacuum injection then can beused to provide an epoxy or other suitable material to fill the openingsin the wafer and form the spacers. In some cases, the epoxy or othermaterial subsequently is cured (e.g., via exposure to heat and/or UVtreatments). The disclosures of the aforementioned US patent documentsare incorporated herein by reference. The processing in FIG. 4E resultsin a second wafer subassembly 450 that provides the bottom substrate 412for each assembly 300.

Next, as shown in FIG. 4F, the first and second wafer subassemblies 440,450 are attached to one another to form a wafer stack 470. Thesubassemblies 440, 450 can be attached to one another, for example, byglue or other adhesive (e.g., by glue jetting or screen printing), andcan be attached to one another such that the optical elements 416, 418face one another. The wafer-level stack 470 then can be separated (e.g.,by dicing) to form multiple individual assemblies 300.

In some instances, in FIG. 4E, the second wafer subassembly 450 can beattached, for example, to UV dicing tape and then diced to form multiplesingulated substrates. The singulated substrates then can be provided toa vacuum injection tool to form the upper and lower spacers 380, 390. Inthat case, the wafer-level method can include attaching the first wafer414 to the singulated substrates to form a stack such that each opticalelement is disposed 416, 418 between the first wafer 414 and one of thesingulated substrates. The stack then is separated (e.g., by dicing)into a plurality of stack assemblies, each of which includes at leastone of the optical elements.

Using a vacuum injection technique to form the spacers 380, 390 can beadvantageous. For example, the addition of the upper spacer 380 allowsthe distance ‘d’ between the optical elements 316, 318 to be increasedeven if the thickness of the lateral side portions 320 of the replicatedmaterial for the optical elements 316, 318 is somewhat limited (e.g.,limited to 50 μm or less in some cases).

In the example process of FIGS. 4A-4F, both wafers 412, 414 have opticalelements 416, 418 replicated on their respective surfaces. In someimplementations, however, only one of the wafers (either the first wafer414 or the second wafer 412) has optical elements on its surface.Further, although the optical elements 416, 418 are shown as DOEs, othertypes of optical elements can be used in some instances.

The stack assemblies 10 (FIG. 1) and 300 (FIG. 3) can be integratedinto, and used with, a wide range of optoelectronic modules. Suchmodules may include active optoelectronic components such as lightemitters (e.g., light emitting diodes (LEDs), infra-red (IR) LEDs,organic LEDs (OLEDs), infra-red (IR) lasers or vertical cavity surfaceemitting lasers (VCSELs)) and/or light sensors (e.g., CCD or CMOSsensor). Further, such modules can be integrated into various types ofconsumer electronics and other devices such as mobile phones, smartphones, personal digital assistants (PDAs), tablets and laptops, as wellas bio devices, mobile robots, and digital cameras, among others.

Various modifications will be readily apparent and are within the spiritof the invention. Thus, other implementations are within the scope ofthe claims.

1. A wafer-level method of fabricating a plurality of stack assemblies,the method comprising: attaching a first wafer to a second wafer to forma wafer sub-stack, wherein at least one of the first wafer or the secondwafer has a plurality of optical elements on its surface, the first andsecond wafers being attached such that each optical element is disposedbetween the first and second wafers; attaching a spacer wafer to thewafer sub-stack to form a wafer stack; and separating the wafer stackinto a plurality of stack assemblies, each of which includes at leastone of the optical elements.
 2. The method of claim 1 wherein each ofthe first and second wafers has a plurality of optical elements on theirrespective surfaces, and wherein each stack assembly includes at leasttwo of the optical elements.
 3. The method of claim 2 wherein attachingthe first and second wafers includes attaching the first and secondwafers to one another through adhesive at lateral side portions of theoptical elements.
 4. The method of claim 1 wherein the optical elementsare diffractive optical elements.
 5. The method of claim 1 wherein theoptical elements are replicated optical elements.
 6. The method of claim1 wherein each stack assembly includes a spacer formed from the spacerwafer to provide a well-defined distance between the at least oneoptical element and a surface on which the stack assembly is to bemounted.
 7. A wafer-level method of fabricating a plurality of stackassemblies, the method comprising: providing first and second wafers,wherein at least one of the first wafer or the second wafer has aplurality of optical elements on its surface; using a single vacuuminjection technique to form upper and lower spacers on opposite surfacesof the second wafer; attaching the first wafer to the second wafer toform a wafer stack, the first and second wafers being attached such thateach optical element is disposed between the first and second wafers;and separating the wafer stack into a plurality of stack assemblies,each of which includes at least one of the optical elements.
 8. Themethod of claim 7 further including forming through-holes in the secondsubstrate, wherein the vacuum injection technique fills thethrough-holes with a same material that forms the upper and lowerspacers.
 9. The method of claim 7, wherein each of the first and secondwafers has a plurality of optical elements on their respective surfaces,and wherein each stack assembly includes at least two of the opticalelements.
 10. The method of claim 7 wherein attaching the first andsecond wafers includes attaching the first and second wafers to oneanother through adhesive disposed between lateral side portions of theoptical elements and the upper spacers on the second wafer.
 11. Themethod of claim 7 wherein the optical elements are diffractive opticalelements.
 12. The method of claim 7 wherein the optical elements arereplicated optical elements.
 13. A stack assembly comprising: a firstsubstrate; a second substrate attached to the first substrate; anoptical element on at least the first substrate or the second substrate,wherein the at least one optical element is disposed between the firstand second substrates; and a first spacer attached to an outer side ofthe first or second substrate.
 14. The stack assembly of claim 13further including a second spacer between the first and secondsubstrates, wherein the first and second spacers are part of a samevacuum injection molded piece.
 15. The stack assembly of claim 13wherein the vacuum injection molded piece laterally surrounds side edgesof the second substrate.
 16. The stack assembly of claim 13 wherein eachof the first and second wafers has a respective optical element on itssurface, the optical elements facing one another.
 17. The stack assemblyof claim 13 wherein each optical element is a diffractive opticalelement.
 18. The stack assembly of claim 13 wherein each opticalelements is a replicated optical element.
 19. The stack assembly ofclaim 13 wherein the first and second substrates are attached to oneanother by adhesive on a lateral side portion of the optical element.20. A wafer-level method of fabricating a plurality of stack assemblies,the method comprising: providing first and second wafers, wherein atleast one of the first wafer or the second wafer has a plurality ofoptical elements on its surface; attaching the second wafer to a tapeand separating the second wafer into a plurality of singulatedsubstrates; placing the singulated substrates into a vacuum injectiontool to form upper and lower spacers on opposite surfaces of thesingulated substrates; attaching the first wafer to the singulatedsubstrates to form a stack such that each optical element is disposedbetween the first wafer and one of the singulated substrates; andseparating the stack into a plurality of stack assemblies, each of whichincludes at least one of the optical elements.